1. Field of the Invention
The present invention relates to a rare earth hexaboride electron-emitting material. More particularly, the present invention relates to a rare earth hexaboride electron-emitting material having long life, which is useful as high intensity thermion emitting material to be used for a scanning electron microscope or an electron image-drawing device.
2. Discussion of Background
Heretofore, single crystals of LaB.sub.6 and CeB.sub.6 have been used as long lasting high intensity thermion emitting materials for electron microscopes or electron image-drawing devices. Further, a (La, Ce)B.sub.6 single crystal as their solid solution, is likewise known to be an excellent electron-emitting material.
Even for such electron-emitting materials having excellent performance, further improvement in their performance have been required in recent years. Particularly, it is desired to develop a thermion emitting material having higher intensity and longer life for a high intensity thermion emitting material.